Dissolved organic nitrogen dynamics in coastal waters and the effect of copepods
نویسندگان
چکیده
15 15 The dynamics of freshly released and N labeled dissolved organic nitrogen (DO N) in the , 94 mm planktonic assemblages of coastal waters and the effects of herbivorous copepods on 15 1 those dynamics were assessed by applying NH under laboratory conditions. At the same time, 4 1 the rate of NH uptake and regeneration in the , 94 mm planktonic assemblages, and the rates of 4 1 15 ingestion and NH regeneration by copepods were evaluated by N accumulation in the 4 15 1 particulate organic nitrogen (PON) fraction and in the copepods, and NH isotope dilution 4 during the incubation. Under conditions of high ambient Chlorophyll a, the presence of copepods 15 stimulated total community DO N release which was correlated with high ingestion rates of the 15 copepods. The copepods primarily grazed on N tagged phytoplankton and ‘sloppy feeding’ 15 would be a mechanism responsible for the DO N release. On the other hand, the addition of 15 copepods gave a negative effect on DO N release in , 94 mm plankton assemblages at the occasions when ambient Chlorophyll a concentrations were low and nitrogen–Chlorophyll a ratios 15 were high. The micrograzer and other organic particles that less labeled by N tracer, would be 15 the important foods for the copepods under those conditions, while the possible DO N release by the micrograzer would be repressed by copepods grazing. When a stimulating effect of the 15 copepods addition on relative DO N accumulation was found, the copepods sometimes released 15 15 more N labeled DON than N assimilated into their body. Even under those conditions, the 15 rates of DO N release by copepods normalized to ambient zooplankton biomass are rather minor compared to those by planktonic assemblages of , 94 mm, suggesting the importance of 15 microzooplankton and phytoplankton on DO N release in this coastal waters. 2000 Elsevier Science B.V. All rights reserved. 15
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تاریخ انتشار 1999